The News From Space Missions Isn't All Bad

IT may have seemed a summer of setbacks for space scientists. But Hubble mirror troubles, shuttle-launch delays, and Magellan Venus spacecraft radio problems not withstanding, there have been successes as well. Moreover, the National Aeronautics and Space Administration (NASA) can thank its European partners for helping to provide the upbeat news.

For one thing, the European Space Agency (ESA) faint-object camera on the Hubble observatory is sending down some remarkable pictures. Images made during an observing period Aug. 23 and 24 show the ring of stellar debris expanding from the supernova that exploded in the Large Magellanic Cloud three years ago. Details are sharp and clear down to a resolution of 0.1 arc seconds.

The cloud is a satellite galaxy of our own Milky Way system. ESA's camera may feel Hubble's blurry focus handicap more strongly when it looks at very distant objects. However, it now is helping Hubble users make the most of what the telescope can accomplish.

What's more important for the summer's space-science record, the ROSAT X-ray satellite is checked out and running well. This German-led mission, with British and United States participation, is a major advance for X-ray astronomy. Indeed, the precision of its X-ray telescope evoked superlatives similar to those that once described the Hubble mirror.

Astronomers focus X-rays by reflecting them at very shallow angles from the surfaces of a set of nested cylinders. ROSAT's reflecting surfaces entered the Guinness Book of Records as the ``smoothest mirror on the world.'' Their average surface roughness is about the diameter of an atom.

Launched June 1, ROSAT lives up to the advance billing. ROSAT scientific director Joachim Tr"umper calls ROSAT's early images ``spectacular.''

X-rays give astronomers a unique view of the cosmos. Electrons spiraling around magnetic-force lines in supernova debris glow with X-ray brilliance. Matter falling in strong gravitational fields can heat to millions of degrees - right in the X-ray energy range. And then there is the diffuse background X-ray glow across the sky, the origin of which is a mystery. It may be very distant galaxies.

X-rays can't penetrate our atmosphere, so astronomers depend on satellites. The last working X-ray observatory - ESA's EXOSAT - failed in April 1986. Until NASA orbits its Advanced X-ray Astronomy Facility later in this decade, ROSAT likely will be the only game in town. But it's quite a game. Its ability to resolve detail is much sharper than its predecessors and its coverage far broader.

Largely a German product, the 2,424-kilogram (2.7 ton) spacecraft carries a British ultraviolet imaging camera and a NASA high-resolution imaging instrument. NASA also paid for the Delta II rocket and launch services. During the initial six months of this 650 million Deutsch mark ($400 million) mission, German scientists will make the first comprehensive X-ray map of the sky. Then the observatory will be available for German, British, and American observers.

Doing science in space is still a technically demanding business. Happily, NASA does not have to face that challenge alone. The agency can work with international partners whose strength and competence help build a record of accomplishment to set against the disappointments.

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